The TcpClient class is a part of the System.Net.Sockets namespace in the C# programming language. It is used to establish a connection to a remote server using the Transmission Control Protocol (TCP). This class allows developers to send and receive data over the network, making it essential for applications that require reliable communication. When a TcpClient object is created, it can connect to a specified IP address and port number. Once connected, developers can use methods like GetStream() to access the underlying network stream for reading and writing data. This makes TcpClient a fundamental tool for network programming in C#.